NRL researchers have developed surface acoustic wave (SAW) sensor systems as noses for gas detection and identification. System detection limits are in the parts per trillion range. The system operates autonomously with a simple gas sampling system and without the need for support gases. Individual SAW devices operate by generating surface mechanical oscillations in piezoelectric quartz, with frequencies in the MHz range. Coating the SAW devices with different polymeric materials (that selectively absorb different gases) allows gas detection by changes in SAW frequency. Arrays of polymer-coated SAW devices detect different gases, and pattern-recognition techniques interpret data and identify unknown(s). SAW sensor systems are currently being used to monitor hazardous chemical vapors, chemical warfare agents, potential fires, and environmental pollutants.